By using a new method, the reverse radar system can improve the distance which can be measured by ultrasonic wave in the condition of using single power. The new system use an infrared receiving chip named CX20106 to deal with the received ultrasonic wave, such as magnification, filtering and shaping. A compensation method is put forward to the error caused by temperature based on analysing the reasons of the errors in the ultrasonic measurement system. The system use the AT89S52 as the MCU to control a low power consumption LCD screen, which is used to display the distance, and a voice circuit is used to alarm.